Duplicated P5CS genes of Arabidopsis play distinct roles in stress
regulation and developmental control of proline biosynthesis
Δ-1-pyrroline-5-carboxylate synthetase enzymes, which catalyse the
rate-limiting step of proline biosynthesis, are encoded by two
closely related P5CS genes in Arabidopsis. Transcription of the
P5CS genes is differentially regulated by drought, salinity and
abscisic acid, suggesting that these genes play specific roles in the
control of proline biosynthesis. Here we describe the genetic
characterization of p5cs insertion mutants, which indicates that P5CS1
is required for proline accumulation under osmotic stress. Knockout
mutations of P5CS1 result in the reduction of stress-induced proline
synthesis, hypersensitivity to salt stress, and accumulation of
reactive oxygen species. By contrast, p5cs2 mutations cause embryo
abortion during late stages of seed development. The desiccation
sensitivity of p5cs2 embryos does not reflect differential control of
transcription, as both P5CS mRNAs are detectable throughout embryonic
development. Cellular localization studies with P5CS–GFP gene fusions
indicate that P5CS1 is sequestered into subcellular bodies in embryonic
cells, where P5CS2 is dominantly cytoplasmic. Although proline feeding
rescues the viability of mutant embryos, p5cs2 seedlings undergo
aberrant development and fail to produce fertile plants even when grown
on proline. In seedlings, specific expression of P5CS2–GFP is seen in
leaf primordia where P5CS1–GFP levels are very low, and P5CS2–GFP also
shows a distinct cell-type-specific and subcellular localization
pattern compared to P5CS1–GFP in root tips, leaves and flower organs. These
data demonstrate that the Arabidopsis P5CS enzymes perform
non-redundant functions, and that P5CS1 is insufficient for
compensation of developmental defects caused by inactivation of P5CS2.
http://www.blackwell-synergy.com/doi/full/10.1111/j.1365-313X.2007.03318.x
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Klaas Vandepoele, PhD
Tel. 32 (0)9 33 13822
VIB Department of Plant Systems Biology, Ghent University
Technologiepark 927, 9052 Gent, Belgium
E-mail: Klaas.Vandepoele@psb.ugent.be
Website: http://bioinformatics.psb.ugent.be/
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